COMPARISON OF IN-VIVO REACTIVATION, IN-VITRO REACTIVATION, AND POLYMERASE CHAIN-REACTION FOR DETECTION OF LATENT PSEUDORABIES VIRUS-INFECTION IN SWINE

The following methods were compared for their ability to detect latent pseudorabies virus in 24 pigs that had been experimentally infected w ith virulent pseudorabies virus: 1) in vivo reactivation by dexamethas one administration, 2) in vitro reactivation by 5 different techniques of explant culture or cocultivation of trigeminal ganglia, and 3) det ection of pseudorabies virus genome in tissue digests of tonsils or tr igeminal ganglia using the polymerase chain reaction. Reactivation of pseudorabies virus by administration of dexamethasone was attempted in 12 of 24 pigs in an effort to determine if this procedure would affec t the detection of latent pseudorabies virus by any of the subsequent in vitro methods. Detection of latent virus by the polymerase chain re action with trigeminal ganglia was the most successful method (24/24 w ere positive). The next most successful method was in vivo reactivatio n through the administration of dexamethasone (10/12 [83%] were positi ve). Only 1 in vitro reactivation technique, cocultivation involving d igestion of the trigeminal ganglia with trypsin and collagenase and th e addition of a hypomethylating agent to the medium, yielded positive results (5/24 [21%] were positive). The polymerase chain reaction perf ormed on tissue digests of tonsils was much less effective (2/24 [8%] were positive) than it was with trigeminal ganglia. Reactivation by de xamethasone did not appear to have any effect on the subsequent detect ion of latency by any of the methods tested.